In recent years, opportunities for listening to music by utilizing a cellular telephone device as an electronic device are increasing. For example, in addition to listening to music by connecting earphones to a cellular telephone device, opportunities for listening to music by causing the speakers disposed in the cellular telephone device to emit sound are increasing. An equalizer being capable of adjusting the sound quality of sound emitted from the speakers to a desired sound quality is built into such a cellular telephone device. Moreover, in addition to listening to music in a state of carrying a cellular telephone device, opportunities for listening to music in the room in a state in which the cellular telephone device is placed on a cradle as a cradle for charging the battery accommodated in the cellular telephone device are also increasing.
Here, a cradle device having a function to play sound produced from a cellular telephone device (a main body of a communication device) has been proposed (for example, Patent Document 1). It is possible to switch the playback by way of outputting a sound signal, which has been output to a playing unit of the cellular telephone device (a main body of a communication device), to a playing unit of the cradle device. In this case, output characteristics are different between the playing unit such as speakers in the cellular telephone device and the playing unit such as speakers in the cradle; therefore, there has been a problem in that the sound quality of produced sound is different before and after switching the playback.
On the other hand, a technique is known for adjusting the sound quality of sound produced from a speaker by adjusting a frequency characteristic of a sound signal with an equalizer. For example, a sheet speaker system has been disclosed that is characterized in that a frequency characteristic of a sound signal is adjusted with an equalizer in order to provide an appropriate sound environment for each sheet speaker, while considering an effect of a sound output (sound signal) in another sheet disposed in the vicinity thereof.
Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2003-32351
Patent Document 2: Japanese Unexamined Patent Application, First Publication No. 2007-065038